In this article, we explore the transfer of functional music as a social control technology from pre-digital to digital media. Muzak, the closest ancestor of online functional music, was expert-designed to improve worker productivity. Ironically, today users themselves are creating mood playlists to enhance their work performance and to manage their emotional states in everyday life contexts. We examine the motivations and practices of users by analyzing their comments on online forums and the descriptions they attach to the mood playlists they create. Our findings indicate that functional music goes through a significant transformation in online media, which brings forth both an expansion of its social control effects and the emergence of novel uses that have a rather ambiguous relationship with social control. We propose that this double mechanism can be used as a basic model for analyzing the interactions between biopower and new media.